1. Field of the Invention
The present invention relates generally to the field of power generation using biological materials. More specifically, the disclosed apparatus and method utilize electrochemical polarization of epithelial cells to generate electricity. Living cells are used to convert chemical energy into electricity. The apparatus is capable of providing long-lasting power to other devices continuously over an extended period of time. Such an apparatus is particularly useful for powering devices that are implanted in the body of an animal or a human, where it may utilize metabolites provided by the host to produce electrical energy without the need for external fuel sources.
2. Description of Related Art
Batteries that utilize biological materials as an integral component are dubbed “biobatteries.” However, it is more appropriate to describe some of these devices as “biogenerators” because they produce electrical power from external sources of continuously supplied biochemical substrates. Although the first such enzyme based device was created in 1964, the underlying principles of operation remain the same. Briefly, enzymes are immobilized onto the anode and/or cathode, which are immersed into an electrolyte containing specific substrates for the enzymes. Chemical reactions occurring at the anode result in loss of electrons by the reactants, while reactions at the cathode result in a net gain of electrons. Thus, a voltage potential is generated between the anode and the cathode. Electrons flow from the anode to the cathode when the two poles are connected, as generally described in Mano et al., A miniature biofuel cell operating in a physiological buffer, J. Am. Chem. Society, 124: 12962-63 (2002).
There is a need to reduce the size of biobatteries while also increasing their service life. Although Mano et al. reported miniaturizing their biobattery while generating about 1.9 mW of electric output at 0.52 V, the battery only lasts for about a week. This relatively short life span may be attributed to the limited supply of substrates inside the battery. For example, the battery designed by Mano et al. uses glucose as a substrate. The battery ceases to produce electricity when the glucose contained inside the battery is depleted. Furthermore, the enzyme-coated electrodes steadily deteriorate and themselves have a limited lifespan.
Another line of research focuses upon cutting the cost of the biobattery/biogenerator. As a result, new types of batteries have been developed which enlist living cells to power the underlying reactions. In one study, live bacterial cells are used in place of more expensive enzymes to catalyze the reactions inside the biogenerator. See e.g., Graham-Rowe, Food scraps could help power homes, New Scientist, issue 2364, Oct. 12, 2002. Although this bacteria-based device may be cheaper to make and could function as a biogenerator using host nutrients, the size of these batteries is close to that of a Walkman cassette player. This size is problematic, for example, in that the size largely precludes use for implantation purposes. Moreover, the use of live bacteria may raise some health concerns when implantation in the host is required.
Many problems remain to be solved before putting these devices into practical use. For biobatteries, both the size and the life span of the device limit the its use as a power source, especially for applications that require implantation of the battery into the human body. For biogenerators, the inclusion of non-human cells such as bacteria in the biogenerator may cause adverse immune response by the host. Therefore, there is a need for a small-sized biogenerator that produces electricity over an extended time without using bacterial cells.